Impact of Ligand Substituents on the Magnetization Dynamics of Mononuclear Dy III Single-Molecule Magnets.

Two mononuclear Dy III single-molecule magnets with different ligand substituents located far from the coordinating atoms, [Dy(L-NO 2 )(NO 3 )] ( 1 ) and [Dy(L-Me)(NO 3 )] ( 2 ), and their diamagnetic-ion diluted analogues, 1' and 2' , were structurally and magnetically characterized. 1 and 2 have nearly identical coordination environments of Dy III ions with D 2d symmetry but different magnetization dynamics. No Orbach process was observed for 1 and 1' in the testing temperature and frequency range, but effective energy barriers of 575 and 829 K for 2 and 2' were obtained, respectively. The opened hysteresis loops were observed until 6 K for 1 and 10 K for 2 . Ab initio calculations reveal that the energy gaps between ground and low-lying excited states of 2 are higher than those of 1 and the relaxation rate through quantum tunneling of magnetization of 2 is lower than that of 1 due to the electronic effect of the axial coordinating oxygen atoms influenced by ligand substitutions.